1. Field of the Invention
This invention relates generally to clamping devices, and, more particularly to a clamping device that clamps a transducer to a pipe using a modified turnbuckle assembly that assures self alignment of the transducer.
2. Discussion of Related Art
The measurement of flow rate within a pipe is important for purposes of maintenance and management of pipeline systems. It is known that an ultrasonic signal can be diagonally passed through the fluid in the pipe to measure fluid flow without intrusion into the pipe. The ultrasonic signal is transmitted from a first transducer and received by a second transducer. In operation, an ultrasonic signal is transmitted from an upstream (with regard to the direction of fluid flow within the pipe) transducer to a downstream transducer and from the downstream transducer to the upstream transducer. In each case, the time between transmission and reception of the ultrasonic signal is measured. The velocity of the fluid flow V.sub.F through the pipe can be determined by the equation: ##EQU1##
wherein Kc is a dimensioned constant(vol/time) related to the pipe, (.DELTA.t) is the difference between the downstream and the upstream transit times, and TL is the average transit time through the fluid.
However, the effect of the fluid flow on the transit times of the downstream and upstream signal is small, so it is essential that an accurate measurement of transit times is made. To determine the transit time of the signal, a phase difference between a reference signal and the received signal may be utilized. Yet, to measure phase difference, the same cycle of the reference and received signals (e.g., a first reference cycle and a first received cycle) should be compared. A comparison between different cycles of the reference and received signals results in misregistration between the reference and the received signal. Misregistration results in a large measurement error in the transit time because the transmitted ultrasonic signal has a relative low time resolution when compared to the upstream/downstream transit times. The ultrasonic signal typically has a period of from hundreds to thousands of nanoseconds while the upstream/downstream transit times are typically from picoseconds to a few nanoseconds. Accordingly, misregistration (e.g., of either the upstream or downstream signal) results in an error in the measurement of the transit time for the misregistered signal (e.g., either downstream or upstream signals) that is much larger than the transit time itself.
In practice, the setup conditions of the transducers including the pipe material, wall thickness, fluid flow rate, etc., affect the received ultrasonic signal. In addition, the beginning of the received signal does not arrive with a sharp leading edge, but rather there is a gradual buildup of the received signal. This is due to a high "Q" (resonance) of the ultrasonic transducer (transmitter) and due to sonic resonance of the pipe wall or other structure through which the ultrasonic signal passes to enter and leave(on the receiving transducer side) the fluid flow.
Clamping such transducers to a respective pipe typically requires a tedious and time consuming procedure. For example, 5 brackets are commonly used to assure that each transducer is properly aligned with the pipe. However, to assure proper alignment, the clamping procedure using brackets takes several minutes or more. In addition, different sized brackets are required depending on the circumference of the pipe.
It is therefore an object of the present invention to overcome the deficiencies of the prior art. Therefore, a need exists for a clamping device for aligning and clamping a transducer to a pipe. A further need exists for a clamping device which is capable of attaching a transducer to a pipe of any size. A still further need exists for a clamping device which is capable of being used for quick, easy and accurate installation on a pipe.